Patterning and fabrication of microstructures within dielectric materials enable a new dimension in material engineering and thus opens up new opportunities for the use of dielectric materials in a variety of applications. The ability to design and process semiconductor materials for integrated circuits (IC) and semiconductor lasers is analogous to such a new dimension and opportunities now presented to dielectric materials.
The feasibility to perform microstructure engineering within dielectric materials has been shown in, for example, domain reversals of ferroelectric materials such as periodically poled lithium niobate (PPLN), periodically poled lithium tantalate (PPLT) and periodically poled KTiOPO4 (PPKTP). Progress has also been shown in other materials such as poling in glass materials or poling in polymer materials.
Example applications of poled dielectric microstructures are quasi-phase-matched (QPM) nonlinear frequency conversion in dielectric materials with second order nonlinear susceptibilities. For example: (1) UV and visible light can be generated via second harmonic generation (SHG) or sum frequency generation (SFG); (2) infrared can be generated via difference frequency generation (DFG), optical parametric oscillation (OPO), optical parametric amplification (OPA) and optical parametric generation (OPG); and (3) optical frequency mixers (OFM) can be used for telecommunication and optical signal processing. Further examples include electro-optic (EO) modulators for beam scanners, sensors, high-speed modulators, etc.
One of the major factors for the realization of the above example applications depends upon the ability to patterning and fabrication of the desired microstructures within the proper materials. The prior art provides a basic patterning and fabrication approach such as ferroelectric domain reversals via electric field poling or thermal poling. However, as the desired patterned structures require finer microstructures such as shorter ferroelectric domain period or pattern structures with aperiodic periods, the challenge in achieving the desired pattern structures arises. Moreover, those methods can't necessarily be used or optimized for the fabrication of several other proper materials. In addition, those methods also might encounter the scalability and yield issues in the fabrication of large area patterned microstructures.
One of the key challenges in the poling of dielectric microstructures is the electric field and electric dipole interference within the body of dielectric materials during the electric field poling process. Such electric field and electric dipole interference results in non-uniform domain structures and difficulties in generating domain with short pitch (period). Additional challenges in poling of dielectric microstructures come from the scalability of the poling area. As the poling area increases, the total required poling time will also increase. The large ratio between the total amount of poling time for large area structures and the optimized poling time for each individual microstructure enhances the fabrication difficulty for generating large area and uniform microstructures.
Other challenges in the poling of dielectric microstructures include the generation of uniform high nucleation density (as seeding in the poling process) under high electric fields and the formation of uniform microstructures under optimized electric fields.
The article “Domain kinetics in the formation of a periodic domain structure in lithium niobate,” V. Y. Shur et al., Physics of the Solid State, Vol. 41, No. 10, pages 1681-1687, October 1999, describes the experimental investigation of the evolution of the domain structure in LiNbO3 with polarization switching in an electric field.
The article “Tunable ultraviolet radiation by second-harmonic generation in periodically poled lithium tantalate,” J. P. Meyn et al., Optics Letters, Vol. 22, No. 16, pages 1214-1216, Aug. 15, 1997, describes electric-field poling of fine-pitch ferroelectric domain gratings in lithium tantalate and characterization of nonlinear-optical properties by single-pass quasi-phase-matched second-harmonic generation (QPM SHG).
The article “Backswitch poling in lithium niobate for high-fidelity domain patterning and efficient blue light generation,” R. G. Batchko et al., Applied Physics Letters, Vol. 75, No. 12, pages 1673-1675, Sep. 20, 1999, describes an electric-field poling technique which incorporates spontaneous backswitching.
The article “Domain in ferroelectric MgO:LiNbO3 by applying electric fields,” A. Kuroda et al., Appl. Physics Lett., 69, pages 1565-1567, Sep. 9, 1996, describes inversion of an antiparallel ferroelectric domain in LiNbO3 doped with 5 mol % MgO (MgO:LN) at room temperature by application of a step-like electric field.
The article “Bulk Periodically Poled MgO-doped LiNbO3 by External Electric Field Application,” M. Nakamura et al., Jpn. J. Appl. Phys., Vol. 38, pages L512-L514, May 1, 1999, describes fabrication of bulk periodically poled MgO-doped LiNbO3 (PPMgLN) crystals by an electric field poling process using a liquid electrode technique.
The article “Bulk periodically poled MgO-LiNbO3 by corona discharge method,” A. Harada et al., Appl. Phys. Lett., 69 (18), pages 2629-2631, Oct. 28, 1996, describes a corona discharge method of the fabrication of bulk periodically poled MgO-LiNbO3 substrates.
The article “Second harmonic generation in electric poled X-cut MgO-doped LiNbO3 waveguides,” S. Sonoda et al., Appl. Phys. Lett., 70 (23), pages 3078-3080, Jun. 9, 1997, demonstrates that quasi-phase-matched second harmonic generation occurs in annealed proton-exchanged (APE) X-cut MgO 5 mol % doped LiNbO3 (MgO:LN) waveguides supporting a TE-mode guided wave.
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